Insights into the Mechanism of Ribosomal Incorporation of Mammalian L13a Protein during Ribosome Biogenesis

Abstract

In contrast to prokaryotes, the precise mechanism of incorporation of ribosomal proteins into ribosomes in eukaryotes is not well understood. For the majority of eukaryotic ribosomal proteins, residues critical for rRNA binding, a key step in the hierarchical assembly of ribosomes, have not been well defined. In this study, we used the mammalian ribosomal protein L13a as a model to investigate the mechanism(s) underlying eukaryotic ribosomal protein incorporation into ribosomes. This work identified the arginine residue at position 68 of L13a as being essential for L13a binding to rRNA and incorporation into ribosomes. We also demonstrated that incorporation of L13a takes place during maturation of the 90S preribosome in the nucleolus, but that translocation of L13a into the nucleolus is not sufficient for its incorporation into ribosomes. Incorporation of L13a into the 90S preribosome was required for rRNA methylation within the 90S complex. However, mutations abolishing ribosomal incorporation of L13a did not affect its ability to be phosphorylated or its extraribosomal function in GAIT element-mediated translational silencing. These results provide new insights into the mechanism of ribosomal incorporation of L13a and will be useful in guiding future studies aimed at fully deciphering mammalian ribosome biogenesis.

SUPPLEMENTAL MATERIAL

Supplemental material for this article may be found at http://dx.doi.org/10.1128/MCB.00250-13.

ACKNOWLEDGMENTS

These studies were supported by PHS grant NIH HL79164 to B.M., AHA Predoctoral Fellowship grants 0815407D and 11PRE7660008 to P.D. and D.P., respectively, NIH predoctoral training fellowship T32HL076125 to the Center for Lung Biology, University of South Alabama, for J.A., NIH AI 059267 to S.B., HFSP RGP0024 to A.A.K., and the Center for Gene Regulation in Health and Disease, sponsored by a Third Frontier grant from the State of Ohio.

We are grateful to Patricia Stanhope Baker for help with manuscript editing and proofreading.

We have no conflicts of interest to declare.